The invention relates to a locking device integrated in a coupling fixed directly onto a ram cylinder for the feeding of the cylinder with a first fluid the circulation of which is controlled by a second fluid, the device comprising (i) a cylindrical member provided with a tightening head at a first end, and with a second threaded end adapted to be engaged into the cylinder, and with an intermediate portion comprised between the first and second ends which is provided with an axial outlet passage towards the cylinder and with a lateral opening terminating at said outlet passage, (ii) a coupling head having a first bore which passes through it, and an internal feed passage through which the first fluid flows, this bore being shaped to receive the intermediate portion and to couple said opening to said feed passage, and (iii) movable internal members intended to modify the circulation of the first fluid by moving under the combined effects of resilient means and a pressure of the second fluid applied to an external locking inlet of the device.
Such devices are used in particular when the pistons or rams, submitted to a permanent loading, must be halted and kept in a predetermined position.